With reference to FAA AC 25-7C, EASA AMC 25. 1581 and the material of some aircraft,this paper studies the method of calculation and validation for the performance degradation relative to configuration deviation list items. Some examples of analysis procedure to the typical items are presented. Except to be satisfied with the safety requirements of airworthiness rules performance degradation information developed with this method in Configuration Deviation List (CDL) should be reasonable and economical.